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.\" Copyright (c) 2016 Martin Matuska

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.Dd December 27, 2016

.Dt TAR 5

.Os

.Sh NAME

.Nm tar

.Nd format of tape archive files

.Sh DESCRIPTION

The

.Nm

archive format collects any number of files, directories, and other

file system objects (symbolic links, device nodes, etc.) into a single

stream of bytes.

The format was originally designed to be used with

tape drives that operate with fixed-size blocks, but is widely used as

a general packaging mechanism.

.Ss General Format

A

.Nm

archive consists of a series of 512-byte records.

Each file system object requires a header record which stores basic metadata

(pathname, owner, permissions, etc.) and zero or more records containing any

file data.

The end of the archive is indicated by two records consisting

entirely of zero bytes.

.Pp

For compatibility with tape drives that use fixed block sizes,

programs that read or write tar files always read or write a fixed

number of records with each I/O operation.

These

.Dq blocks

are always a multiple of the record size.

The maximum block size supported by early

implementations was 10240 bytes or 20 records.

This is still the default for most implementations

although block sizes of 1MiB (2048 records) or larger are

commonly used with modern high-speed tape drives.

(Note: the terms

.Dq block

and

.Dq record

here are not entirely standard; this document follows the

convention established by John Gilmore in documenting

.Nm pdtar . )

.Ss Old-Style Archive Format

The original tar archive format has been extended many times to

include additional information that various implementors found

necessary.

This section describes the variant implemented by the tar command

included in

.At v7 ,

which seems to be the earliest widely-used version of the tar program.

.Pp

The header record for an old-style

.Nm

archive consists of the following:

.Bd -literal -offset indent

struct header_old_tar {

	char name[100];

	char mode[8];

	char uid[8];

	char gid[8];

	char size[12];

	char mtime[12];

	char checksum[8];

	char linkflag[1];

	char linkname[100];

	char pad[255];

};

.Ed

All unused bytes in the header record are filled with nulls.

.Bl -tag -width indent

.It Va name

Pathname, stored as a null-terminated string.

Early tar implementations only stored regular files (including

hardlinks to those files).

One common early convention used a trailing "/" character to indicate

a directory name, allowing directory permissions and owner information

to be archived and restored.

.It Va mode

File mode, stored as an octal number in ASCII.

.It Va uid , Va gid

User id and group id of owner, as octal numbers in ASCII.

.It Va size

Size of file, as octal number in ASCII.

For regular files only, this indicates the amount of data

that follows the header.

In particular, this field was ignored by early tar implementations

when extracting hardlinks.

Modern writers should always store a zero length for hardlink entries.

.It Va mtime

Modification time of file, as an octal number in ASCII.

This indicates the number of seconds since the start of the epoch,

00:00:00 UTC January 1, 1970.

Note that negative values should be avoided

here, as they are handled inconsistently.

.It Va checksum

Header checksum, stored as an octal number in ASCII.

To compute the checksum, set the checksum field to all spaces,

then sum all bytes in the header using unsigned arithmetic.

This field should be stored as six octal digits followed by a null and a space

character.

Note that many early implementations of tar used signed arithmetic

for the checksum field, which can cause interoperability problems

when transferring archives between systems.

Modern robust readers compute the checksum both ways and accept the

header if either computation matches.

.It Va linkflag , Va linkname

In order to preserve hardlinks and conserve tape, a file

with multiple links is only written to the archive the first

time it is encountered.

The next time it is encountered, the

.Va linkflag

is set to an ASCII

.Sq 1

and the

.Va linkname

field holds the first name under which this file appears.

(Note that regular files have a null value in the

.Va linkflag

field.)

.El

.Pp

Early tar implementations varied in how they terminated these fields.

The tar command in

.At v7

used the following conventions (this is also documented in early BSD manpages):

the pathname must be null-terminated;

the mode, uid, and gid fields must end in a space and a null byte;

the size and mtime fields must end in a space;

the checksum is terminated by a null and a space.

Early implementations filled the numeric fields with leading spaces.

This seems to have been common practice until the

.St -p1003.1-88

standard was released.

For best portability, modern implementations should fill the numeric

fields with leading zeros.

.Ss Pre-POSIX Archives

An early draft of

.St -p1003.1-88

served as the basis for John Gilmore's

.Nm pdtar

program and many system implementations from the late 1980s

and early 1990s.

These archives generally follow the POSIX ustar

format described below with the following variations:

.Bl -bullet -compact -width indent

.It

The magic value consists of the five characters

.Dq ustar

followed by a space.

The version field contains a space character followed by a null.

.It

The numeric fields are generally filled with leading spaces

(not leading zeros as recommended in the final standard).

.It

The prefix field is often not used, limiting pathnames to

the 100 characters of old-style archives.

.El

.Ss POSIX ustar Archives

.St -p1003.1-88

defined a standard tar file format to be read and written

by compliant implementations of

.Xr tar 1 .

This format is often called the

.Dq ustar

format, after the magic value used

in the header.

(The name is an acronym for

.Dq Unix Standard TAR . )

It extends the historic format with new fields:

.Bd -literal -offset indent

struct header_posix_ustar {

	char name[100];

	char mode[8];

	char uid[8];

	char gid[8];

	char size[12];

	char mtime[12];

	char checksum[8];

	char typeflag[1];

	char linkname[100];

	char magic[6];

	char version[2];

	char uname[32];

	char gname[32];

	char devmajor[8];

	char devminor[8];

	char prefix[155];

	char pad[12];

};

.Ed

.Bl -tag -width indent

.It Va typeflag

Type of entry.

POSIX extended the earlier

.Va linkflag

field with several new type values:

.Bl -tag -width indent -compact

.It Dq 0

Regular file.

NUL should be treated as a synonym, for compatibility purposes.

.It Dq 1

Hard link.

.It Dq 2

Symbolic link.

.It Dq 3

Character device node.

.It Dq 4

Block device node.

.It Dq 5

Directory.

.It Dq 6

FIFO node.

.It Dq 7

Reserved.

.It Other

A POSIX-compliant implementation must treat any unrecognized typeflag value

as a regular file.

In particular, writers should ensure that all entries

have a valid filename so that they can be restored by readers that do not

support the corresponding extension.

Uppercase letters "A" through "Z" are reserved for custom extensions.

Note that sockets and whiteout entries are not archivable.

.El

It is worth noting that the

.Va size

field, in particular, has different meanings depending on the type.

For regular files, of course, it indicates the amount of data

following the header.

For directories, it may be used to indicate the total size of all

files in the directory, for use by operating systems that pre-allocate

directory space.

For all other types, it should be set to zero by writers and ignored

by readers.

.It Va magic

Contains the magic value

.Dq ustar

followed by a NUL byte to indicate that this is a POSIX standard archive.

Full compliance requires the uname and gname fields be properly set.

.It Va version

Version.

This should be

.Dq 00

(two copies of the ASCII digit zero) for POSIX standard archives.

.It Va uname , Va gname

User and group names, as null-terminated ASCII strings.

These should be used in preference to the uid/gid values

when they are set and the corresponding names exist on

the system.

.It Va devmajor , Va devminor

Major and minor numbers for character device or block device entry.

.It Va name , Va prefix

If the pathname is too long to fit in the 100 bytes provided by the standard

format, it can be split at any

.Pa /

character with the first portion going into the prefix field.

If the prefix field is not empty, the reader will prepend

the prefix value and a

.Pa /

character to the regular name field to obtain the full pathname.

The standard does not require a trailing

.Pa /

character on directory names, though most implementations still

include this for compatibility reasons.

.El

.Pp

Note that all unused bytes must be set to

.Dv NUL .

.Pp

Field termination is specified slightly differently by POSIX

than by previous implementations.

The

.Va magic ,

.Va uname ,

and

.Va gname

fields must have a trailing

.Dv NUL .

The

.Va pathname ,

.Va linkname ,

and

.Va prefix

fields must have a trailing

.Dv NUL

unless they fill the entire field.

(In particular, it is possible to store a 256-character pathname if it

happens to have a

.Pa /

as the 156th character.)

POSIX requires numeric fields to be zero-padded in the front, and requires

them to be terminated with either space or

.Dv NUL

characters.

.Pp

Currently, most tar implementations comply with the ustar

format, occasionally extending it by adding new fields to the

blank area at the end of the header record.

.Ss Numeric Extensions

There have been several attempts to extend the range of sizes

or times supported by modifying how numbers are stored in the

header.

.Pp

One obvious extension to increase the size of files is to

eliminate the terminating characters from the various

numeric fields.

For example, the standard only allows the size field to contain

11 octal digits, reserving the twelfth byte for a trailing

NUL character.

Allowing 12 octal digits allows file sizes up to 64 GB.

.Pp

Another extension, utilized by GNU tar, star, and other newer

.Nm

implementations, permits binary numbers in the standard numeric fields.

This is flagged by setting the high bit of the first byte.

The remainder of the field is treated as a signed twos-complement

value.

This permits 95-bit values for the length and time fields

and 63-bit values for the uid, gid, and device numbers.

In particular, this provides a consistent way to handle

negative time values.

GNU tar supports this extension for the

length, mtime, ctime, and atime fields.

Joerg Schilling's star program and the libarchive library support

this extension for all numeric fields.

Note that this extension is largely obsoleted by the extended

attribute record provided by the pax interchange format.

.Pp

Another early GNU extension allowed base-64 values rather than octal.

This extension was short-lived and is no longer supported by any

implementation.

.Ss Pax Interchange Format

There are many attributes that cannot be portably stored in a

POSIX ustar archive.

.St -p1003.1-2001

defined a

.Dq pax interchange format

that uses two new types of entries to hold text-formatted

metadata that applies to following entries.

Note that a pax interchange format archive is a ustar archive in every

respect.

The new data is stored in ustar-compatible archive entries that use the

.Dq x

or

.Dq g

typeflag.

In particular, older implementations that do not fully support these

extensions will extract the metadata into regular files, where the

metadata can be examined as necessary.

.Pp

An entry in a pax interchange format archive consists of one or

two standard ustar entries, each with its own header and data.

The first optional entry stores the extended attributes

for the following entry.

This optional first entry has an "x" typeflag and a size field that

indicates the total size of the extended attributes.

The extended attributes themselves are stored as a series of text-format

lines encoded in the portable UTF-8 encoding.

Each line consists of a decimal number, a space, a key string, an equals

sign, a value string, and a new line.

The decimal number indicates the length of the entire line, including the

initial length field and the trailing newline.

An example of such a field is:

.Dl 25 ctime=1084839148.1212\en

Keys in all lowercase are standard keys.

Vendors can add their own keys by prefixing them with an all uppercase

vendor name and a period.

Note that, unlike the historic header, numeric values are stored using

decimal, not octal.

A description of some common keys follows:

.Bl -tag -width indent

.It Cm atime , Cm ctime , Cm mtime

File access, inode change, and modification times.

These fields can be negative or include a decimal point and a fractional value.

.It Cm hdrcharset

The character set used by the pax extension values.

By default, all textual values in the pax extended attributes

are assumed to be in UTF-8, including pathnames, user names,

and group names.

In some cases, it is not possible to translate local

conventions into UTF-8.

If this key is present and the value is the six-character ASCII string

.Dq BINARY ,

then all textual values are assumed to be in a platform-dependent

multi-byte encoding.

Note that there are only two valid values for this key:

.Dq BINARY

or

.Dq ISO-IR\ 10646\ 2000\ UTF-8 .

No other values are permitted by the standard, and

the latter value should generally not be used as it is the

default when this key is not specified.

In particular, this flag should not be used as a general

mechanism to allow filenames to be stored in arbitrary

encodings.

.It Cm uname , Cm uid , Cm gname , Cm gid

User name, group name, and numeric UID and GID values.

The user name and group name stored here are encoded in UTF8

and can thus include non-ASCII characters.

The UID and GID fields can be of arbitrary length.

.It Cm linkpath

The full path of the linked-to file.

Note that this is encoded in UTF8 and can thus include non-ASCII characters.

.It Cm path

The full pathname of the entry.

Note that this is encoded in UTF8 and can thus include non-ASCII characters.

.It Cm realtime.* , Cm security.*

These keys are reserved and may be used for future standardization.

.It Cm size

The size of the file.

Note that there is no length limit on this field, allowing conforming

archives to store files much larger than the historic 8GB limit.

.It Cm SCHILY.*

Vendor-specific attributes used by Joerg Schilling's

.Nm star

implementation.

.It Cm SCHILY.acl.access , Cm SCHILY.acl.default, Cm SCHILY.acl.ace

Stores the access, default and NFSv4 ACLs as textual strings in a format

that is an extension of the format specified by POSIX.1e draft 17.

In particular, each user or group access specification can include

an additional colon-separated field with the numeric UID or GID.

This allows ACLs to be restored on systems that may not have complete

user or group information available (such as when NIS/YP or LDAP services

are temporarily unavailable).

.It Cm SCHILY.devminor , Cm SCHILY.devmajor

The full minor and major numbers for device nodes.

.It Cm SCHILY.fflags

The file flags.

.It Cm SCHILY.realsize

The full size of the file on disk.

XXX explain? XXX

.It Cm SCHILY.dev, Cm SCHILY.ino , Cm SCHILY.nlinks

The device number, inode number, and link count for the entry.

In particular, note that a pax interchange format archive using Joerg

Schilling's

.Cm SCHILY.*

extensions can store all of the data from

.Va struct stat .

.It Cm LIBARCHIVE.*

Vendor-specific attributes used by the

.Nm libarchive

library and programs that use it.

.It Cm LIBARCHIVE.creationtime

The time when the file was created.

(This should not be confused with the POSIX

.Dq ctime

attribute, which refers to the time when the file

metadata was last changed.)

.It Cm LIBARCHIVE.xattr. Ns Ar namespace Ns . Ns Ar key

Libarchive stores POSIX.1e-style extended attributes using

keys of this form.

The

.Ar key

value is URL-encoded:

All non-ASCII characters and the two special characters

.Dq =

and

.Dq %

are encoded as

.Dq %

followed by two uppercase hexadecimal digits.

The value of this key is the extended attribute value

encoded in base 64.

XXX Detail the base-64 format here XXX

.It Cm VENDOR.*

XXX document other vendor-specific extensions XXX

.El

.Pp

Any values stored in an extended attribute override the corresponding

values in the regular tar header.

Note that compliant readers should ignore the regular fields when they

are overridden.

This is important, as existing archivers are known to store non-compliant

values in the standard header fields in this situation.

There are no limits on length for any of these fields.

In particular, numeric fields can be arbitrarily large.

All text fields are encoded in UTF8.

Compliant writers should store only portable 7-bit ASCII characters in

the standard ustar header and use extended

attributes whenever a text value contains non-ASCII characters.

.Pp

In addition to the

.Cm x

entry described above, the pax interchange format

also supports a

.Cm g

entry.

The

.Cm g

entry is identical in format, but specifies attributes that serve as

defaults for all subsequent archive entries.

The

.Cm g

entry is not widely used.

.Pp

Besides the new

.Cm x

and

.Cm g

entries, the pax interchange format has a few other minor variations

from the earlier ustar format.

The most troubling one is that hardlinks are permitted to have

data following them.

This allows readers to restore any hardlink to a file without

having to rewind the archive to find an earlier entry.

However, it creates complications for robust readers, as it is no longer

clear whether or not they should ignore the size field for hardlink entries.

.Ss GNU Tar Archives

The GNU tar program started with a pre-POSIX format similar to that

described earlier and has extended it using several different mechanisms:

It added new fields to the empty space in the header (some of which was later

used by POSIX for conflicting purposes);

it allowed the header to be continued over multiple records;

and it defined new entries that modify following entries

(similar in principle to the

.Cm x

entry described above, but each GNU special entry is single-purpose,

unlike the general-purpose

.Cm x

entry).

As a result, GNU tar archives are not POSIX compatible, although

more lenient POSIX-compliant readers can successfully extract most

GNU tar archives.

.Bd -literal -offset indent

struct header_gnu_tar {

	char name[100];

	char mode[8];

	char uid[8];

	char gid[8];

	char size[12];

	char mtime[12];

	char checksum[8];

	char typeflag[1];

	char linkname[100];

	char magic[6];

	char version[2];

	char uname[32];

	char gname[32];

	char devmajor[8];

	char devminor[8];

	char atime[12];

	char ctime[12];

	char offset[12];

	char longnames[4];

	char unused[1];

	struct {

		char offset[12];

		char numbytes[12];

	} sparse[4];

	char isextended[1];

	char realsize[12];

	char pad[17];

};

.Ed

.Bl -tag -width indent

.It Va typeflag

GNU tar uses the following special entry types, in addition to

those defined by POSIX:

.Bl -tag -width indent

.It "7"

GNU tar treats type "7" records identically to type "0" records,

except on one obscure RTOS where they are used to indicate the

pre-allocation of a contiguous file on disk.

.It "D"

This indicates a directory entry.

Unlike the POSIX-standard "5"

typeflag, the header is followed by data records listing the names

of files in this directory.

Each name is preceded by an ASCII "Y"

if the file is stored in this archive or "N" if the file is not

stored in this archive.

Each name is terminated with a null, and

an extra null marks the end of the name list.

The purpose of this

entry is to support incremental backups; a program restoring from

such an archive may wish to delete files on disk that did not exist

in the directory when the archive was made.

.Pp

Note that the "D" typeflag specifically violates POSIX, which requires

that unrecognized typeflags be restored as normal files.

In this case, restoring the "D" entry as a file could interfere

with subsequent creation of the like-named directory.

.It "K"

The data for this entry is a long linkname for the following regular entry.

.It "L"

The data for this entry is a long pathname for the following regular entry.

.It "M"

This is a continuation of the last file on the previous volume.

GNU multi-volume archives guarantee that each volume begins with a valid

entry header.

To ensure this, a file may be split, with part stored at the end of one volume,

and part stored at the beginning of the next volume.

The "M" typeflag indicates that this entry continues an existing file.

Such entries can only occur as the first or second entry

in an archive (the latter only if the first entry is a volume label).

The

.Va size

field specifies the size of this entry.

The

.Va offset

field at bytes 369-380 specifies the offset where this file fragment

begins.

The

.Va realsize

field specifies the total size of the file (which must equal

.Va size

plus

.Va offset ) .

When extracting, GNU tar checks that the header file name is the one it is

expecting, that the header offset is in the correct sequence, and that

the sum of offset and size is equal to realsize.

.It "N"

Type "N" records are no longer generated by GNU tar.

They contained a

list of files to be renamed or symlinked after extraction; this was

originally used to support long names.

The contents of this record

are a text description of the operations to be done, in the form

.Dq Rename %s to %s\en

or

.Dq Symlink %s to %s\en ;

in either case, both

filenames are escaped using K&R C syntax.

Due to security concerns, "N" records are now generally ignored

when reading archives.

.It "S"

This is a

.Dq sparse

regular file.

Sparse files are stored as a series of fragments.

The header contains a list of fragment offset/length pairs.

If more than four such entries are required, the header is

extended as necessary with

.Dq extra

header extensions (an older format that is no longer used), or

.Dq sparse

extensions.

.It "V"

The

.Va name

field should be interpreted as a tape/volume header name.

This entry should generally be ignored on extraction.

.El

.It Va magic

The magic field holds the five characters

.Dq ustar

followed by a space.

Note that POSIX ustar archives have a trailing null.

.It Va version

The version field holds a space character followed by a null.

Note that POSIX ustar archives use two copies of the ASCII digit

.Dq 0 .

.It Va atime , Va ctime

The time the file was last accessed and the time of

last change of file information, stored in octal as with

.Va mtime .

.It Va longnames

This field is apparently no longer used.

.It Sparse Va offset / Va numbytes

Each such structure specifies a single fragment of a sparse

file.

The two fields store values as octal numbers.

The fragments are each padded to a multiple of 512 bytes

in the archive.

On extraction, the list of fragments is collected from the

header (including any extension headers), and the data

is then read and written to the file at appropriate offsets.

.It Va isextended

If this is set to non-zero, the header will be followed by additional

.Dq sparse header

records.

Each such record contains information about as many as 21 additional

sparse blocks as shown here:

.Bd -literal -offset indent

struct gnu_sparse_header {

	struct {

		char offset[12];

		char numbytes[12];

	} sparse[21];

	char    isextended[1];

	char    padding[7];

};

.Ed

.It Va realsize

A binary representation of the file's complete size, with a much larger range

than the POSIX file size.

In particular, with

.Cm M

type files, the current entry is only a portion of the file.

In that case, the POSIX size field will indicate the size of this

entry; the

.Va realsize

field will indicate the total size of the file.

.El

.Ss GNU tar pax archives

GNU tar 1.14 (XXX check this XXX) and later will write

pax interchange format archives when you specify the

.Fl -posix

flag.

This format follows the pax interchange format closely,

using some

.Cm SCHILY

tags and introducing new keywords to store sparse file information.

There have been three iterations of the sparse file support, referred to

as

.Dq 0.0 ,

.Dq 0.1 ,

and

.Dq 1.0 .

.Bl -tag -width indent

.It Cm GNU.sparse.numblocks , Cm GNU.sparse.offset , Cm GNU.sparse.numbytes , Cm  GNU.sparse.size

The

.Dq 0.0

format used an initial

.Cm GNU.sparse.numblocks

attribute to indicate the number of blocks in the file, a pair of

.Cm GNU.sparse.offset

and

.Cm GNU.sparse.numbytes

to indicate the offset and size of each block,

and a single

.Cm GNU.sparse.size

to indicate the full size of the file.

This is not the same as the size in the tar header because the

latter value does not include the size of any holes.

This format required that the order of attributes be preserved and

relied on readers accepting multiple appearances of the same attribute

names, which is not officially permitted by the standards.

.It Cm GNU.sparse.map

The

.Dq 0.1

format used a single attribute that stored a comma-separated

list of decimal numbers.

Each pair of numbers indicated the offset and size, respectively,

of a block of data.

This does not work well if the archive is extracted by an archiver

that does not recognize this extension, since many pax implementations

simply discard unrecognized attributes.

.It Cm GNU.sparse.major , Cm GNU.sparse.minor , Cm GNU.sparse.name , Cm GNU.sparse.realsize

The

.Dq 1.0

format stores the sparse block map in one or more 512-byte blocks

prepended to the file data in the entry body.

The pax attributes indicate the existence of this map

(via the

.Cm GNU.sparse.major

and

.Cm GNU.sparse.minor

fields)

and the full size of the file.

The

.Cm GNU.sparse.name

holds the true name of the file.

To avoid confusion, the name stored in the regular tar header

is a modified name so that extraction errors will be apparent

to users.

.El

.Ss Solaris Tar

XXX More Details Needed XXX

.Pp

Solaris tar (beginning with SunOS XXX 5.7 ?? XXX) supports an

.Dq extended

format that is fundamentally similar to pax interchange format,

with the following differences:

.Bl -bullet -compact -width indent

.It

Extended attributes are stored in an entry whose type is

.Cm X ,

not

.Cm x ,

as used by pax interchange format.

The detailed format of this entry appears to be the same

as detailed above for the

.Cm x

entry.

.It

An additional

.Cm A

header is used to store an ACL for the following regular entry.

The body of this entry contains a seven-digit octal number

followed by a zero byte, followed by the

textual ACL description.

The octal value is the number of ACL entries

plus a constant that indicates the ACL type: 01000000

for POSIX.1e ACLs and 03000000 for NFSv4 ACLs.

.El

.Ss AIX Tar

XXX More details needed XXX

.Pp

AIX Tar uses a ustar-formatted header with the type

.Cm A

for storing coded ACL information.

Unlike the Solaris format, AIX tar writes this header after the

regular file body to which it applies.

The pathname in this header is either

.Cm NFS4

or

.Cm AIXC

to indicate the type of ACL stored.

The actual ACL is stored in platform-specific binary format.

.Ss Mac OS X Tar

The tar distributed with Apple's Mac OS X stores most regular files

as two separate files in the tar archive.

The two files have the same name except that the first

one has

.Dq ._

prepended to the last path element.

This special file stores an AppleDouble-encoded

binary blob with additional metadata about the second file,

including ACL, extended attributes, and resources.

To recreate the original file on disk, each

separate file can be extracted and the Mac OS X

.Fn copyfile

function can be used to unpack the separate

metadata file and apply it to th regular file.

Conversely, the same function provides a

.Dq pack

option to encode the extended metadata from

a file into a separate file whose contents

can then be put into a tar archive.

.Pp

Note that the Apple extended attributes interact

badly with long filenames.

Since each file is stored with the full name,

a separate set of extensions needs to be included

in the archive for each one, doubling the overhead

required for files with long names.

.Ss Summary of tar type codes

The following list is a condensed summary of the type codes

used in tar header records generated by different tar implementations.

More details about specific implementations can be found above:

.Bl -tag -compact -width XXX

.It NUL

Early tar programs stored a zero byte for regular files.

.It Cm 0

POSIX standard type code for a regular file.

.It Cm 1

POSIX standard type code for a hard link description.

.It Cm 2

POSIX standard type code for a symbolic link description.

.It Cm 3

POSIX standard type code for a character device node.

.It Cm 4

POSIX standard type code for a block device node.

.It Cm 5

POSIX standard type code for a directory.

.It Cm 6

POSIX standard type code for a FIFO.

.It Cm 7

POSIX reserved.

.It Cm 7

GNU tar used for pre-allocated files on some systems.

.It Cm A